It's going to depend on how hard you're going to hit the card, but the GTX n70 is usually the sweet spot for price and performance when it comes to rendering. The 970 is a bit high, seems to average about $320 or so after sales and rebates (but other retailers might have other sales and there are other models, personally I like EVGA) If you really MUST be under that $300 mark, the 770 is going to be better than the 960. However, I wouldn't go too far back, while you could likely get a 590 near your budget you're likely going to lose compute power (and the benchmarks of the 590 vs. the 970 show computer performance is easily 30% higher on the 970)

If you do happen to choose to go AMD, I would suggest the W5000/5100 as Peter mentioned, it's going to give you the best mix of memory and crunching power, but if you're going to be heavy into Adobe then odds are you'll do better going nvidia as it's more optimized and you should get quicker renders.

Ultimately:

It's going to be what you're working on and how long you're willing to wait for renders.

I'm using a "top end" EVGA 650ti (so a bit faster, double the memory), but I tend to really just crank things out in photoshop. The little work I do in premiere is pretty basic, so when I do renders (1080p/30, Youtube Suggested Bitrates) I end up with renders taking about 1.5x the length of the final product and that's acceptable to me. The biggest bottleneck I've run into is really overflowing the memory and having to rely on system memory or the scratch disk so my only suggestion is that whatever you settle on, make sure that if there is an option for the same model but with more memory that you opt for that (that and if you don't have one, pick up a cheap ~60gb SSD and assign it as scratch, it does wonders)

Thanks for the AMD mentions! Jaivendra, welcome to the community :) As others have shared, AMD has some great GPU products such as AMD FirePro for workstation applications. Our FirePro line is a diverse line-up of products designed to meet your needs. Here's some more information on the W5000 and the W5100 that others have recommended. Let me know if I can help answer any questions!